Pipe end closure assemblies are known. These are typically in the form of a plug arranged to slide into a pipe end, and provided with a means for securing the plug into the pipe end whereby the plug grips the inner wall of the pipe and also forms a seal between the plug body and the inner wall of the pipe.
A typical prior art closure assembly may have a tapped rod extending through a tubular plug providing a gripping and sealing assembly, the tapped rod provided with a plate for fitting inside the pipe at its distal end and passing through a bush in an end-cap at its proximal end, the plate and end-cap sandwiching the tubular plug. A nut on the proximal end may be tightened to force the plate and end-cap towards each other, in order to squeeze the tubular plug in use after insertion of the distal end of the closure assembly into the pipe end. The closure assembly may be slid into an open pipe end in an un-squeezed arrangement, distal end first, and then one or more elastomeric washer seals, gripping rings and/or anti-extrusion means for the seals of the tubular plug may be urged radially outwards against the inner wall. For instance, the elastomeric washer will be squeezed radially outwards to form a seal against the inner face of the pipe, and inverse collet arrangements may be used to cause the gripping means and/or anti-extrusion means to expand radially when axially compressed, in order to enable the closure assembly to grip the inner wall of the pipe and to prevent undesired extrusion of elastomer.
One problem with such prior art arrangements is that they are tightened to grip and seal by screwing, and this may require high torques to be applied to the closure assembly. This may be difficult to achieve in hostile environments such as the undersea environment, where human divers, manned undersea vehicles or remotely operated undersea vehicles may be needed to put the closure assembly in place. There is also a risk that the torque applied to the pipe end as the nut is tightened to form the seal may result in damage to the pipe, weakening it, breaking it or increasing risk of future breakage.
Another problem with the prior art apparatus and methods is that the terminated pipe end may be subject to extremely high forces acting radially outwards from the central axis of the assembly where the plug is squeezed against the inner face of the pipe. The pipe walls may thus be subject to continuous bending or shear stresses after the closure assembly has been put in place to terminate a pipe end, and this may eventually give rise to fatigue stress cracking or fracture of the pipe.
Furthermore, there is limited multiple redundancy, to protect against seal failure of seal or gripping means, built into the prior art arrangements. Although multiple seals or multiple gripping collets may be used to provide a back-up in case one seal or gripping means fails, the length of the tubular plug may be limited by the desire to reduce the torque required to tighten the plug, and so multiple redundancies may be limited. Also, any failure arising from, for instance, unevenness of the inner face of the pipe, is likely to give rise to failure in the secondary seal/grip if it gives rise to failure in a primary seal/grip, and so independence of alternative seals and gripping means is desirable.
Hence there is a need for a closure assemblies and closure methods for providing fluid-tight termination of pipe ends, capable of withstanding high pressure differences across the termination, particularly for pipe ends in hostile environments, which address or overcome some or all of the problems in the prior art.